Passenger vehicle transport capacity is an important design aspect of modern vehicles. The ability to haul objects and equipment is often as important as the vehicle's ability to transport additional passengers. Solutions aimed at increasing a vehicle's hauling capabilities must not only be directed at improving the vehicle's utility but must also be directed towards improving a vehicle's safety and performance while accomplishing this task. One traditional approach towards improving a vehicle's transport capabilities has been through the addition of a trailer attached to the vehicle. Trailers allow for a wide range of items to be transported by a vehicle, often without impacting transport capabilities of the vehicle's passenger compartment.
Passenger vehicles commonly control trailer braking through the use of a trailer brake controller located within the vehicle. The trailer is commonly equipped with electrically actuated trailer brakes. An operator sets the gain on the controller, where the gain dictates how much electrical output is generated by the controller for a given set of vehicle inputs. The controller utilizes a brake input signal in combination with the user set gain to generate a brake control signal. It is known that this signal can take different forms, such as a duty cycle output or DC voltage output. This control signal is sent to the electrically actuated brakes which are thereby utilized to effectuate braking within the trailer. Systems such as described translate vehicle input, such as brake pedal force or position, brake pressure or vehicle acceleration, into a brake control signal which is adjustable according to the operator set gain. The brake control output signal, in turn, energizes the trailer brakes, which subsequently generates a braking torque on the trailer wheels.
Although the aforementioned systems may benefit from a lack of complexity, they fail to address the real world principles of mechanics that electrically actuated dual-servo drum brake assemblies are subject to. At increased velocities, it is known that the effectiveness of dual-servo brake torque is reduced and therefore a given brake control signal generates less effective brake torque at higher vehicle speeds than it did at lower vehicle speeds. As such, trailer brake performance degenerates at higher vehicle speeds. It would be highly desirable to have a trailer brake control apparatus and method that compensated for the loss of effective brake torque at increased vehicle speeds such that a consistent brake torque could be generated over the entire range of expected vehicle speeds.
It is further known, that a brake torque desirable over a broad range of vehicle speeds may be undesirable at low vehicle speeds. At low vehicle speeds, electric dual-servo drum braking systems are subject to significant increases in effectiveness wherein an applied brake torque may result in the brakes locking up (also known as “grabbiness”) rather than incrementally applying braking friction. Existing electric trailer braking systems commonly fail to address this known phenomenon and thereby produce undesirable vehicle low-speed results. It would, therefore, be highly desirable to have a trailer braking system that improved low-speed performance by reducing brake-grab.
Finally, if one is to consider vehicle speed in the development of a brake control signal, it is important to consider the issues involved with accurate velocity calculation. Measurement of vehicle velocity based on wheel speed is subject to a host of errant readings due to automotive performance conditions. During rapid deceleration, it is known that a wheel may generate excessive slip relative to the road surface. In such circumstances, if vehicle speed was estimated based solely on this wheel in deep slip, the estimate would be lower than the actual vehicle speed. Similarly in rapid acceleration if a wheel breaks away from the road surface it may result in a velocity value abnormally high. In other circumstances, such as vehicle turns, outer wheels may experience a velocity increase while inner wheels a decrease. Thus it would be further beneficial to develop an improved method of calculating vehicle speed prior to its utilization in effecting the trailer brake control signal.